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Am stuck !! Pls help !!

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by candygal79 » Wed Mar 26, 2014 8:33 pm
2. If Sally can paint a house in 4 hours, and John can paint the same house in 6 hour, how long will it take for both of them to paint the house together?

A. 2 hours and 24 minutes
B. 3 hours and 12 minutes
C. 3 hours and 44 minutes
D. 4 hours and 10 minutes
E. 4 hours and 33 minutes

My workout :

1/4 +1/6 = 5/12 , am stuck after this .
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by Brent@GMATPrepNow » Wed Mar 26, 2014 10:31 pm
candygal79 wrote:2. If Sally can paint a house in 4 hours, and John can paint the same house in 6 hour, how long will it take for both of them to paint the house together?

A. 2 hours and 24 minutes
B. 3 hours and 12 minutes
C. 3 hours and 44 minutes
D. 4 hours and 10 minutes
E. 4 hours and 33 minutes
Rule #1: If a person can complete an entire job in k hours, then in one hour, the person can complete 1/k of the job
Example: If it takes Sue 5 hours to complete a job, then in one hour, she can complete 1/5 of the job. In other words, her work rate is 1/5 of the job per hour

Rule #2: If a person completes a/b of the job in one hour, then it will take b/a hours to complete the entire job
Example: If Sam can complete 1/8 of the job in one hour, then it will take him 8/1 hours to complete the job.
Likewise, if Joe can complete 2/3 of the job in one hour, then it will take him 3/2 hours to complete the job.

Now onto the question...
Sally can paint a house in 4 hours, and John can paint the same house in 6 hours
So, according to green rule, Sally paints 1/4 of the house in 1 hour, and John paints 1/6 of the house in 1 hour
COMBINED, the fraction of the house they can paint in 1 hour = 1/4 + 1/6
= 3/12 + 2/12
= 5/12
So, they can paint 5/12 of the house in 1 hour

If they can paint 5/12 of the house in 1 hour, then according to blue rule, they can paint ENTIRE house in 12/5 hours.
12/5 hours = 2 2/5 hours
= 2 hours and a bit
= A

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Brent
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by Brent@GMATPrepNow » Wed Mar 26, 2014 11:27 pm
candygal79 wrote:2. If Sally can paint a house in 4 hours, and John can paint the same house in 6 hour, how long will it take for both of them to paint the house together?

A. 2 hours and 24 minutes
B. 3 hours and 12 minutes
C. 3 hours and 44 minutes
D. 4 hours and 10 minutes
E. 4 hours and 33 minutes
Alternatively, we can use a bit of logic.

Notice that John is the SLOWER painter.

John can paint the same house in 6 hours
So, if John were to work with ANOTHER painter who painted at the SAME SPEED, the two identical painters could paint the house half the time.
In other words, they could paint the house in 3 hours.

Since Sally can paint FASTER than John, then John and Sally would be able to paint the house even faster than John and an identical painter.
In other words, John and Sally would be able to paint the house in LESS than 3 hours.

Since only answer choice A is less than 3 hours, the correct answer is A

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by [email protected] » Thu Mar 27, 2014 12:24 am
Hi candygal79,

This question involves 2 people working on a job together, so it's perfect for the Work Formula:

Work = (AxB)/(A+B)

A and B represent the amount of time that it takes each person to paint the house:

A = 4 hours
B = 6 hours

Now plug in...

(4x6)/(4+6) = 24/10 hours

2.4 hours = 2 hours 24 minutes

Final Answer: A

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by GMATGuruNY » Thu Mar 27, 2014 3:25 am
candygal79 wrote:2. If Sally can paint a house in 4 hours, and John can paint the same house in 6 hour, how long will it take for both of them to paint the house together?

A. 2 hours and 24 minutes
B. 3 hours and 12 minutes
C. 3 hours and 44 minutes
D. 4 hours and 10 minutes
E. 4 hours and 33 minutes
Let the house = 12 units.
Since Sally can paint 12 units in 4 hours, Sally's rate = w/t = 12/4 = 3 units per hour.
Since John can paint 12 units in 6 hours, John's rate = w/t = 12/6 = 2 units per hour.
Combined rate for Sally and John = 3+2 = 5 units per hour.
Time for Sally and John together to paint 12 units = w/r = 12/5 hours = 2 hours, 24 minutes.

The correct answer is A.
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Am stuck !! Pls help !!

by Brent@GMATPrepNow » Wed Jan 10, 2018 7:11 am
candygal79 wrote:2. If Sally can paint a house in 4 hours, and John can paint the same house in 6 hour, how long will it take for both of them to paint the house together?

A. 2 hours and 24 minutes
B. 3 hours and 12 minutes
C. 3 hours and 44 minutes
D. 4 hours and 10 minutes
E. 4 hours and 33 minutes
We can solve this question quickly by using a little number sense.

Sally can paint a house in 4 hours
So, if there were TWO Sallys, they'd be able to paint the house in HALF the time.
In other words, TWO Sallys could paint the house in 2 hours

John can paint the same house in 6 hours
So, if there were TWO Johns, they'd be able to paint the house in HALF the time.
In other words, TWO Johns could paint the house in 3 hours

So, the time it takes Sally and John to paint the house will be BETWEEN 2 hours and 3 hours

This allows us to eliminate B, C, D, and E

Answer: A
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by GMATWisdom » Wed Jan 10, 2018 7:27 am
candygal79 wrote:2. If Sally can paint a house in 4 hours, and John can paint the same house in 6 hour, how long will it take for both of them to paint the house together?

A. 2 hours and 24 minutes
B. 3 hours and 12 minutes
C. 3 hours and 44 minutes
D. 4 hours and 10 minutes
E. 4 hours and 33 minutes

My workout :

1/4 +1/6 = 5/12 , am stuck after this .
1/4+1/6=5/12 is ok. that means 5/12 th work is done by both in one hour, so complete work will be done in 1/(5/12)=12/5 hours which is equal to 2hours and 24 minutes.
hope no more confusion left.
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